A collocation study of atmospheric motion vectors (AMVs) compared to Aeolus wind profiles with a feature track correction (FTC) observation operator

A method to apply an empirical feature track correction (FTC) in a new observation operator for atmospheric motion vectors (AMVs) is proposed. The FTC AMV observation operator determines the background estimate of the observed AMV vector wind, adjusting the background profile by determining an optimal height adjustment, averaging the profile over a layer of optimal thickness, and applying a linear correction to the averaged profile wind. The FTC observation operator is tested in the context of a collocation study between AMVs projected onto the collocated Aeolus horizontal line‐of‐sight (HLOS) and the Aeolus HLOS wind profiles. This study is a prototype for a variational FTC for numerical weather prediction data assimilation systems in which the Aeolus wind profiles take the place of the background in the FTC observation operator. Compared to a collocation where the Aeolus profile is interpolated linearly in height to the AMV height, a simple ad hoc averaging approach and the FTC approach reduce the mean square difference between the AMV observation and the Aeolus estimated AMV observation by 38% and 43%, respectively. A feature track correction (FTC) observation operator for atmospheric motion vectors (AMVs) is proposed and tested. The FTC has four degrees of freedom corresponding to wind speed multiplicative and additive corrections (γ and δV), an estimate of the depth of the layer that contributes to the AMV (Δz), and a vertical height assignment correction (h). In practice, a regular vertical grid results in discretized values for Δz and h. As a result, optimizing these four parameters requires an inner optimization for γ and δV that uses the standard linear model and an outer optimization (pictured) for Δz and h that uses a brute force search. In a collocation study in terms of horizontal line‐of‐sight vector winds (HLOSV), in which the Aeolus HLOSV profiles take the place of the background in the FTC observation operator, the variance of the misfit is reduced by 43%.